Question

Which is more efficient

if(!var_name)

or

if(var_name == NULL)

Answer 1

Both will compile to the same code. Your choice of which to use should depend on which is most readable.

This version:

if(var_name == NULL)

should only be used when var_name is a pointer, otherwise you will confuse anyone who reads your code in the future. Some compilers might complain if you use this on a non-pointer.

This one:

if(!var_name)

should be used in cases when you are logically treating var_name as a boolean (true/false) value. This can include when var_name is a pointer, since NULL is the value for “false” or undefined pointers.

If var_name is an integer, then I would choose a third option:

if(var_name == 0)

as I find it expresses intent more clearly.